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An Introductory Review for U-fa (USM Driven Woofer) Development

It was twelve years ago, the concept of “U-fa” was born. Since then, a lot of people carry the torch up to today. This paper was originally intended to the phantom AES/NY convention in 2001 but it was shelved since. However, the second revival of the activity brought several Japanese convention papers already and the first world debut was made in AES/NY last October.
Since audio world and Ultrasonic Motor has little to share a common ground, it seems difficult to appreciate what actually make difference by introducing USM to Woofer. In order to bridge the gap, original paper is refurbished totally. Emphasis is put on to introductory reading for the background, rather than theories and equations.